no spark

Hey Guys, new to the board, looking for some advice. Recently purchased a clean 82 750 Maxim. Had trouble starting if i didn't start it for a few days(started fine when warm). When it did start, it would have an intermittent miss. Now it won't start at all (cranks fine, good speed), Pulled a plug and layed it against the head with the wire on during cranking and i have no spark, sometimes a weak one or two after i let off the start button and the engines winding down. What would be the first things i should check and the procedure to diagnose them. I'd hate to just start buying parts without some idea where the problem lies. Thanks in advance for your help, this is a great site.

Chris

 

Welcome to you. Make sure your battery is fully charged. This is very important to proper spark. I suppose it goes without saying that you should have a book on this bike handy when you start this process, things will go much smoother.

Pop the seat. Check your ignition fuse. Fuse box on these bikes is a regular corrosion problem. Got 12 VDC (battery voltage actually)? If not, you need to replace the fuse or fix the fuse holder.Otherwise, proceed.

Next, check the coils. Make sure you've got 12 VDC reaching the coils. No? Your ignition circuit may be broken somewhere (starter switch, ignition switch), you'll need to chase the 12 volts down.
If you have the requisite 12 volts, ohm out the primary (2 to 3 ohms) and secondary (11 Kohms approximately) resistance on both coils. These tend to drop dead when they get about this old.
Don't fret if you find an unhappy resistance reading, it happens. This simply means your needing new ones and will need about $130 for a new set from Accel or a little more for the Dynas. If your readings are good, I'm going to suggest testing your TCI unit.
Enough for now, check out your machine and get back to us. Best of luck to you.

 

Check sidestand switch linkage for possible binding. Un-plug non-neutral safety relay and test for starting. Relay is on center of frame below tank closest to front of seat securing knotch.

Shoot a spritz of WD-40 in the slot of the ignition switch and the Kill switch; too.

I'm crossing my fingers for you ... hoping it's as simple as replacing a 20-year-old relay!

We'll get you rolling again. You can take that to the bank!

 

And looky at the fuzes.....

 

Thanks for the quick responses guys, just got back from the garage, here's what i got. I pulled the fuse cover and everything is in check, nothing blown and no corrosion. It's spotless and even has the two spares in the cover, bike's in real nice shape. I have 12 volts at the battery (even threw the charger on trickle and bumped it up to 13), still nothing. Pulled the tank off to get to the coils. Obvious to you guys i have 2 coils, one on the right has a red w/white stipe and grey wires and the one on the left has a red w/white stripe and orange wire. Which one am i checking for 12 volts? Is that with the key on or actually cranking? Also to ohm out the coils, where am i acually checking with my tester leads for primary and secondary resistance? I assume one of the tests is across the small wires in the front of the coils but i'd just like to make sure. Thanks again for all your help guys.

Chris

 

82yam750 , and hi by the way , before goin in too deep , just check to see if all the volts are in the correct spot with a test ight or multimeter..

ie:12v at the coils with key on and then at startup ect ,as 1 wire is a fixed 12v.

Also at the tci unit if you have one...

 

Hey first off welcome to the site and I hope the forums can offer the help that you need, Ihave found it a great place of information, and BS...lol had to throw that one in there. As far as the spark, I would check like metioned previously, battery charge, mine did the same as yours until I replace an old battery, did you test Batt voltage under load, it may be fine sitting there with no draw, but it may drop off signifigantly when put under load. Check volts while cranking see if they drop off to far. If this is the casechange battery and try again. If not check wires and follow the ignition system unplug wires, bad grounds, or split wires can all cause a problem, check your coil pos wire for open short to ground as well. We'll get ya up and running just keep us updated.

 

Yep ... you have to check those grounds.

Checking the Primary's is across both of the small gauge wires going into the coils. I've done some Yamaha and Honda coil checking and didn't get much resistance across the Primary (sometimes the meter didn't even budge) ... but, the Primary was good.

You need to have the full resistance across the Secondary's. You check the striped wire to the cap connection in the spark plug wire.

The odds of finding a bad coil are pretty small. The odds that you'll find both coils bad are astronomical. So, if you think its a bad coil ... swap the plastic connections out between the coils and the opposite two cylinders should fire.

I really want you to check-out the safety relay. The safety relay shuts-down the spark when the sidestand is down or the bike is in gear without the clutch lever being pulled.

That safety relay is specific to the safety circuit. The wiring to the safety relay is NOT the same as relays for lights, horns and flashers.

If you think of the four blades inside the standard relay as signal voltage across the top two ... with the switched circuit being the bottom two ... the safety relay takes the signal voltage across the two on the left and the switched circuit on the right. (or vice-versa) You just need to know the difference.

You can test the relay with some wires off a 9V Smoke detector battery. You'll hear or feel -- or both -- the relay clicking or closing.

If you undo that relay and it fires-up ... I'll check my bike for the exact wiring and numbers on the relay.

So ... you need to try to start the bike with the sidestand UP and the clutch lever PULLED. If it fires-up that relay is bad.

If the bike wants to start or the starter motor engages --- let's be sure to get this right, now ...

If the starter motor kicks-in and turns-over the engine when the clutch lever is RELEASED with the bike IN GEAR when you PRESS the START button ... the SAFETY relay is either NO GOOD -- or -- NOT a safety relay ... but rather a STANDARD relay ... and MUST be swapped-out for a SAFETY Relay!

 

Ok, here's where i'm at. I discovered i have spark if i hold the plug an 1/8 inch away from the engine. No spark when the side of the plug touches it. I put it together and crank, crank, crank, nothing. Pull the plugs, spray starter fluid in the cylinders and it starts and dies. Do it again and i get it running. After it's warm it starts again no problem. Here's the thing, when i rev the engine, the rpms jump to 5 grand or so and stay there for about 6 or 7 seconds. It's not a mechanical problem with the throttle cable, it's closing all the way. Vacuum leak? I don't see how? The rubber boots are in perfect shape and i sprayed carb cleaner around them to make sure there was no rpm change. Also, the bike won't run if the choke is touched at all, it dies the second you touch it. There doesn't seem to be any kind of accelerator pump on the carbs either. Making it even harder to start when it's cold. Are any of these problems linked together? Thanks again for all your help guys.

Chris

 

Make sure your plugs are gapped at 0.028 to 0.032 (thousands of an inch). No spark with the plug grounded but a spark from the threads to ground indicates an internally shorted or fouled plug. Pop a new set of plugs in.
High lingering RPM after a goose of the throttle suggests a very rich fuel mixture (if your certain there are no other factors such as throttle cable routing or binding).
There is no accelerator pump on these things. Just a fuel enrichment circuit, erroniously referred to as a choke. Is it possible your choke cable is installed with no slack in it, causing the plungers to remain open?
What color are your plugs Chris? If they are blackened, your carbs are in need of adjustment. Otherwise, I'm fresh out of ideas.
Be sure to invest in a maintenance manual (any one will do, I prefer the Haynes myself) and hit the troubleshooting matrix, helpful little bugger. Unfortunately, like so many problems with vehicles, the problem is usually very easy to find if your standing in front of the beast. I wish we could do a live feed on this site just to be able to listen and see the machine in action.

 

Given the new information; I would say you have two problems.

1) Vacuum Piston Stiction ... I was going to type "Moderate" ... but, the truth is: "You got it BAD"

You need to dive into the carbs sometime soon.

The NO Start, in my opinion, is related to the Upper Carb fuel suction SIPHON -- (The little brass tube you have to line-up with the hole for it on the FUEL BOWL.

The SIPHON Tubes are clogged ... or, the METERING PORTS that supply fuel to the SIPHON WELL on the fuel bowl are clogged. You're not drawing fuel up the ENRICHMENT CIRCUIT and the bike won't start without a RICH MIXTURE.

This is a very COMMON PROBLEM, particularily with bikes that haven't moved for some time.

If the metering ports at the bottom of the fuel bowl are clogged ... these TINY metering "Jets" need to be cleaned-out with an appropriate tool.

Neither Seafoam nor Carb Cleaner blessed by the Pope is going to unclog them if they are stuffed or clogged shut. Nothing's moving through those ports until you work-out the stoppage with a tool.

Search the archives for: "Clunk Test" to understand the problem and the easy remedy.

We'll try knocking-off every possible issue that's keeping you in the Pits and not out on the track.

Eye's kallin on dem evil sputz tuh git out chore bike. Eye's kallin on da pow-eh huff duh oily spirit to geh yezz sim magik MOJO woikin fur ya'll.

OK ... the MOJO's working ... Let's get that thing running!

 

Ok, took the carbs off. Pulled the tops and bowls off them one at a time. Sanded the large brass slides and their bores with some 1000 grit to clean them up. Ran some fine wire, carb cleaner and air through both jets, thin brass feed tube on the bowl side,and both the jets under the large diaphram area in the top. Pulled the enriching needles out after sliding out the bar, ran carb cleaner and air through them. I ran carb cleaner and air through the float needle and seat being carfull not to disturb it's setting. The slides pass the "clunk" test with flighing colors (they actually did before i took them apart though). Is there anything else i should do before i put this back on the bike? All the rubber boots are perfect and have all their caps on them.
Also, what is the correct procedure to start this bike, turn the petcock to PRI, start the bike and then to RUN? Besides the main idle knob, i don't see any adjustment to these carbs, are they behind plugs that need to be drilled? Right now i'd be happy with starting without starting fuid, am i overlooking anything? Thanks in advance, we'll get this thing going!!!

Chris

 

Chris ...

You do have to drill them ... stick a sheet metal screw in the drill hola and pop them out of there.

Beware! The plug is thinner than a dime and will drill-through with ease as it it brass. DO NOT allow the drill to penetrate much beyond the plug ... as the soft, brass, slotted Pilot Screw is just beyond the plug.

The factory setting of those Pilot Screws is generally accepted to be two and one-half turns OUT from bottoming-out the Screw.

You'll want to apply some light oil and use a screwdriver that fits the screw slot with extreme precision to prevent breaking-off the shoulders of the slot.

It is also widely accepted by the members, here, that the Factory setting is too lean. You will do well to re-adjust those Pilot Screws to a setting closer to three full turns out ... or maybe just a little bit beyond.

This causes me to have a Brain-Storm ... as I recently adjusted my Pilot Screws with the ColorTune Plug.

It might serve everyone well for me to check the setting that the Screw is at, now, after ColorTuning ... to allow that value to be a BASE adjustment for those who have recently over-hauled and cleaned their carbs. The precision attained by ColorTuning is Dead-On. The "New" Pilot Screw adjustment out measurement will be invaluable to those needing a set-up point after the cleaning work.

It was like a bolt of lightning striking me. I wish the lightning charge would have lasted a bit longer so I could have ColorTuned to a nice Blue rather than the lean mixture is seems to have coming from the factory!

 

This is gunna show my inexperience, but where on the carbs is the plug that hides the pilot screws? Also, will i be able to reach them when the bike is all backtogether with the tank on and bike running? Thanks again guys.

Chris

 

Looking at the carbs as they fit into the cylinder head; the Pilot Screws are on the top, just to the inside of the Enrichment Valve. They may or may not be concealed by a small, brass anti-tamper plug.

(Why is it called an Anti-tamper Plug? A better name might be Anti-fine-tuning Plug.)

 

Ok, did a very thorough cleaning, spending about a half hour on each carb. Drilled out the caps over the pilot screws, cleaned them and set them at 3 turns out. Put in new plugs, started right up. Runs like a top. Idle was way high because of my previous attempts to keep in running in the past i had it bumped up. The fact that it was high i think was a good sign, showing it's running correctly now. Readjusted the idle and took it out for a 20 min ride. Nice power and very smooth. This bike really makes some power when you get around 3,500 rpm, really takes off. After the 20min ride, got back and headlight was dim, battery pretty drained. Just read the post about the alternator brushes so that's my next project. Big thanks to Rick, Robert and everyone else who gave me a hand, great work guys!

Chris

 

where's this post about the alternator brushes? I am having trouble finding it right now.

Thanks.

 

Here's one link

http://www.xjbikes.com/Forums/viewtopic ... ushes.html

 

thanks man..I just couldn't find what I was looking for even with the searching. oh well, it was late last night for me.

Thanks.